Is a tasty fish a healthy fish?

The landscape appeared to be on fire that clear, crisp fall day. The Indigenous community had come to engage in the fish tasting event, a communal get-together hosted by the mine’s environment department. This meeting had been held regularly at the same cabin overlooking a lake for over a decade. Each year, people of different backgrounds gathered to assess the health of fish downstream of mining operations and to determine if those fish continue to be safe to eat. At past engagements, community members had shared fish-related concerns, including declining populations, deteriorating health, and changing taste. The land’s elders had applied traditional knowledge, learned over many generations, to angle and net fish from mine-impacted waters the day before. One of the elders representing the community assessed the condition and health of a fish twice as long and ten times heavier than the filleting knife that lay on the cutting board. The fish appeared healthy, but would the taste and texture of the fish be acceptable to community members?

The lethally sampled fish looked normal compared to the other fish on ice in the cooler—clearish eyes, abrasion-free scales, and uneroded fins. Still, a closer observation under the operculum revealed unusually pale, swollen gills intertwined with a few tapeworms.

“Did the mine cause this?” enquired an elder.

“Parasitic infections are common in fish, and some parasites, particularly tapeworms, can influence nutrient uptake and decrease the amount of energy available for growth and reproduction,” replied the mine’s environmental coordinator as he scanned the shoreline for bears that the smell of the fish might attract.

“Treated effluent discharged into lakes downstream of the mine may have contributed to eutrophication — excessive nutrient richness — and contained contaminants that affected the manifestation of parasites,” an invited fisheries biologist contracted by the mine’s environment department chimed in. “For example, mine explosives contain nitrogen

compounds — nitrogen compounds are nutrients — those nutrients can cause excessive plant growth. In turn, excessive plant growth can lead to decreased oxygen levels, which can then kill fish. The prevalence and species of parasites are available in the mine’s environmental monitoring program reports. Still, I’ll take photos to document this observation and collect a subsample of its gills using the sterile tools in my dissecting kit and preserve them in formalin for further analyses.”

“I would be honoured to assess the internal viscera of this fish,” continued the biologist, who proceeded, following nods of approval from the elders, to make a ventral incision from the anus to the gill slit and pin the tissue flaps. “This fish is likely a ripe female because egg-like structures are visible within the ovary, though sex is determined using a dissecting microscope and confirmed by histology analysis. I can collect its gonads and preserve them in formalin until analyses of mean egg size and fecundity. By fecundity, we mean the number of eggs per female fish; this is an indicator of reproductive health.”

“Its internal organs seem normal — black spleen ventral to the stomach, red kidney along the length of the vertebral column, and olive gall bladder posterior to the liver. The stomach is also full of smaller fish, which shows this fish was eating well. The only organ that stands out to me is the liver; it’s enlarged with more of a ‘coffee with creme’ colour than its characteristic red hue. The liver is a fish’s principal detoxifying organ, and an enlarged liver may indicate that the body is ridding itself of contaminants. I think collecting the liver for analysis would be valuable.” The biologist placed the organ in formalin.

“Shall we also collect fin clips and ear stones to find out how old this fish is?” she asked. Following unanimous agreement, a pectoral fin was clipped, wrapped in wax paper, and placed in a labelled envelope. The paired otoliths were then carefully removed from the fish’s skull and placed in a separate labelled envelope. “These bony structures will be read by a specialist in fish ageing who interprets patterns in cross-sections and counts alternating light and dark growth rings, just like aging a tree,” she explained.

“Arsenic, lead, and mercury have been detected in tissues collected from fish in the area, but reported concentrations were well below consumption guidelines,” she continued, sealing the envelope of otoliths. “This fish is a good size, meaning it’s old and has been

around for a while, so it may have measurable levels of mercury as this metal biomagnifies within food chains. Might I suggest collecting the dorsal muscle from the left side because this tissue is targeted for metal storage, and it is the most edible part of the fish? If this fish were alive, I would anesthetize it and collect a biopsy punch, also called a tissue plug, from the same area. I would then put the sample in a plastic bag on ice until it could be properly frozen, apply an antibiotic ointment to the biopsied area, and return the fish to the same location where it was captured as quickly as possible.”

“If you’re concerned about contamination, I can seal a whole filet in a labelled plastic bag and freeze the sample when we return to the mine, then ship it on ice to a laboratory for fish tissue chemistry analysis later today.” suggested the mine’s environmental coordinator.

“Good idea.” the biologist replied, “Fish tissue chemistry results, or body burdens of contaminants may explain the effects observed during this fish health assessment and provide an early warning of changes in the quality of edible fish.”

The elders, having a lifetime of experience living on the land, were pleased with the description of the sampling and analyses. Then, it was their turn to bring their expertise to play. To begin, they evaluated the texture of the fish flesh before them and reported their observations using a scoring system from very good or above average health to not good or below average health. All assessed fish were given a moderate rating; they were neither exceptionally good nor were they causing concern for eating. One of the elders proceeded to prepare the red- and orange-tinged fillets by boiling them in clean water – this is, water in which no oils, spices, or other mediums commonly used to make food more flavourful had been added. The participants were asked to taste the boiled fish and assess using the same scoring system as before. Scores given to these boiled fillets were above moderate. One of the tasters described the meat as “melt-in-your-mouth.”

Based on this information, is a tasty fish a healthy fish? Fish tasting events are an important complement to fish health and fish tissue chemistry programs. A fish may be safe for consumption based on scientific guidelines, yet its taste and texture considered unacceptable to community members. Taste alone, however, does not incorporate other

health-related endpoints – things such as parasite presence and abundance, enlarged or discolored liver, and empty stomachs – that could be indication industrial activities affecting growth, reproduction, or survival of the fish. These indices used in conjunction provide the best approach to fish health assessments.

Guest blog writer: Lindsey Felix